The 50th Street Station, one of the stops for the No. 1 line in Manhattan, is not one of the newest, cleanest, brightest subway stops in New York City’s labyrinthine system. Nor am I going to argue that this tile mosaic in the station’s waiting area, which I photographed this weekend, is one of the world’s great works of art. Still, it’s representational and, more to the point for tired, beleaguered commuters, cheerful. One more, admittedly small, thing to be thankful for this week.